Metal-based drugs have gained significant importance in medicine in recent years. In this research, a series of new Co(II), Ni (II), Cu (II), Zn(II), and Ru(III) complexes of a Schiff base ligand, (1,5-dimethyl-4-((1-(3-nitrophenyl)ethylidene) amino)-2-phenyl-1,2-dihydro-3H-pyrazol-3-one), were prepared for the first time in excellent yields, and characterized by elemental analysis, FT-IR, 1H NMR, 13C NMR, ICP-OES, and thermal analysis. The in vitro antiproliferative, anticholinesterase, and antioxidant properties of complexes 1–5 were evaluated. The cytotoxic effects of complexes 1–5 on the viability of colon cancer (DLD-1), breast cancer (MDA-MB-231), and healthy lung (Wl-38) cell lines were investigated using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) method in vitro. The anticancer activities of the ligand and its metal complexes were lower than those of the reference drug, cisplatin. In anticholinesterase activity studies, complex 4 (88.46±0.45% inhibition) in butyrylcholinesterase (BChE) assay showed a higher inhibitory effect than the standard compound galanthamine with 78.14±0.55% inhibition. In antioxidant assays, some complexes showed higher antioxidant activities than standard antioxidant butylated hydroxytoluene (BHT). Among the prepared complexes, complex (4) (IC50=5.91±0.17 µM) in ABTS assay showed the highest antioxidant activity compared to BHT (IC50=16.19±0.17 µM). Also, this complex (IC50=10.17±0.36 µM) showed the best antioxidant activity in CUPRAC assay compared to BHT (IC50=39.37±0.12 µM).